provide writeto_then_readfrom only if needed

Author: caternuson

adafruit_tca9548a.py

@@ -57,6 +57,9 @@ class TCA9548A_Channel():
     def __init__(self, tca, channel):
         self.tca = tca
         self.channel_switch = bytearray([1 << channel])
+        # provide only if needed
+        if hasattr(self.tca.i2c, 'writeto_then_readfrom'):
+            setattr(self, 'writeto_then_readfrom', self.writeto_then_readfrom_passthru)
 
     def try_lock(self):
         """Pass thru for try_lock."""
@@ -82,7 +85,7 @@ def writeto(self, address, buffer, **kwargs):
             raise ValueError("Device address must be different than TCA9548A address.")
         return self.tca.i2c.writeto(address, buffer, **kwargs)
 
-    def writeto_then_readfrom(self, address, buffer_out, buffer_in, **kwargs):
+    def writeto_then_readfrom_passthru(self, address, buffer_out, buffer_in, **kwargs):
         """Pass thru for writeto_then_readfrom."""
         #In linux, at least, this is a special kernel function call
         if address == self.tca.address: